[{AgL}₂Mo₈O₂₆]^n- complexes: a combined experimental and theoretical study

Area of Science:

• Coordination Chemistry
• Supramolecular Chemistry
• Materials Science

Background:

• Polyoxometalates (POMs) are versatile anionic metal-oxide clusters with diverse structures and properties.
• Silver(I) ions are known to form complexes with various ligands, influencing their coordination environment and reactivity.
• The self-assembly of POMs with metal ions offers pathways to novel functional materials.

Purpose of the Study:

• To synthesize and characterize novel silver-ligand-polyoxometalate complexes using different ligands and POM precursors.
• To investigate the structural diversity and coordination behavior of silver ions within these complexes.
• To explore potential intermolecular interactions, such as halogen bonding, and the solution behavior of the synthesized complexes.

Main Methods:

• Self-assembly reactions in N,N-Dimethylformamide (DMF) solvent.
• Isolation and characterization of products using X-ray diffraction (XRD), Infrared (IR) spectroscopy, and elemental analysis.
• Quantum Theory of Atoms in Molecules (QTAIM) analysis for coordination sphere evaluation.
• Density Functional Theory (DFT) calculations for halogen bonding energy estimation.
• High-Performance Liquid Chromatography coupled with Inductively Coupled Plasma-Atomic Emission Spectrometry (HPLC-ICP-AES) for solution behavior studies.

Main Results:

• Formation of [β-{AgL}₂Mo₈O₂₆]^2- anions (where L = PPh₃, PPh₂Py, AsPh₃, SbPh₃) isolated as Bu₄N⁺ salts.
• Observation of silver(I) ion coordination number switching (5 to 6) based on ligand type (e.g., SbPh₃ with DMF uptake).
• Isolation of novel complexes with substituted pyridine ligands, including those exhibiting halogen bonding (3-X-pyridine ligands).
• DFT calculations provided estimated energies for halogen bonding interactions (0.9–3.4 kcal mol^-1).
• HPLC-ICP-AES studies indicated significant dissociation of the [β-{AgL}₂Mo₈O₂₆]^2- anions in acetonitrile solution.
• A different POM precursor, [Mo₆O₁₉]^2-, yielded the complex [Ag₂(PyPPh₂)₂(DMF)₄][Mo₆O₁₉].

Conclusions:

• The self-assembly approach provides a versatile route to novel silver-ligand-polyoxometalate architectures.
• Ligand choice significantly influences the coordination environment around silver and the overall complex structure.
• Halogen bonding interactions can be present and quantified in these POM complexes, adding another layer of structural complexity.
• The synthesized POM complexes exhibit considerable dissociation in solution, relevant for their potential applications.